1. Field of the Invention
The present invention relates to an O-ring seal of a small-sized geared-motor which is to be used as an actuator of a conveyer or a machine tool and has a reduction gear head mounted detachably from a motor unit.
2. Description of the Prior Art
Machines and tools used in the industrial world have diversified in recent years. Particularly, in the field of geared-motors wherein a motor unit and a reduction gear head are integrated, the number of combinations of motor units and reduction gear heads, is very large. Additionally, motor units are functionally classified, while reduction gear heads are classified by the reduction gear ratio. Therefore, generally, the motor units and the reduction gear heads of geared motors are stored separately. A motor unit and a reduction gear head, which are respectively selected for satisfying the aim, are subsequently assembled as a geared-motor for actual use.
Typically a grease-bath lubrication system is adopted in the lubrication of the reduction gear head of the geared-motor. A geared-motor using such a lubrication system is free from the restriction of the orientation of the mounting of the geared-motor and its lubrication is easy. Furthermore, noise-reduction of the reduction gear and extension of the service time period of the geared-motor can be achieved by adopting a grease-bath lubrication system. For sealing the coupling portion of the motor unit and the reduction gear head of the geared-motor, an O-ring seal is widely used.
A conventional O-ring seal of the geared-motor is described referring to FIGS. 3, 4 and 5. FIG. 3 is a cross-sectional side view of the conventional geared-motor having an O-ring seal. In FIG. 3, a conventional geared motor consists of a motor unit 50 and a reduction gear-head 51.
The reduction gear head 51 comprises: a reduction gear train 1 having an output shaft 1a and gears 1b, 1c, 1d, 1e and 1f; plural bearings 16, 17, 18, 19 . . . for bearing the output shaft 1a and gear shafts 1g and 1h; and an oil seal 13 for sealing lubricant grease 15 so as not to leak out from the gaps between the output shaft 1a and the gear case 2.
The motor unit 50 comprises: a frame 3; a stator core 4 which is fit to and fixed on an inner face 3b of the frame 3; a bracket 7 which is press-fit to an upper end of the inner face 3b; bearings 8 and 9 respectively provided on a center hole 7a of the bracket 7 and a center hole 3a of the frame 3 for bearing a rotor shaft 5; a rotor assembly 6 which is fixed to the rotor shaft 5; a brake system 11 provided on bottom parts of the rotor assembly 6 and the frame 3; and an oil seal 14 provided between the rotor shaft 5 and the bracket 7 so as not to leak out the lubricant grease 15 from inside of the gear case 2 of the reduction gear head 51 to inside of the frame 3 of the motor unit 50. An O-ring 20 is provided between an outer periphery of a circular boss 7c of the bracket 7 and a bevel 2b of the gear case 2.
FIG. 4 is a perspective view showing the construction of the seal part of the conventional geared motor. In FIG. 4, the motor unit 50 and the reduction gear head 51 are connected by plurality of screw bolts 31 and nuts 30.
FIG. 5 is an enlarged cross-sectional side view showing a seal part of the conventional geared-motor of FIG. 3 designated by "Y". In FIG. 5, an outer face 7d of the circular boss 7c of the bracket 7 fits to the inner face 2a of the gear case 2 for centering the rotor shaft 5. The rotor shaft 5 must be positioned substantially at the center of the motor unit 50 for coupling a gear part 5a of the rotor shaft with the initial gear 1f of the reduction gear train 1. The bevel 2b is formed in a bottom end part of the inner face 2a of the gear case 2. The O-ring 20 is pinched by the bevel 2b of the gear case 2, the outer face 7d of the circular boss 7c and a flange face 7b of the bracket 7. The O-ring 20 is deformed by a compressive force which is the result of fixing the reduction gear head 51 to the motor unit 50 by the screw bolts 31 and the nuts 30 (shown in FIGS. 3 and 4). Thereby, in most cases, the deformed O-ring 20 tightly seals the inside of the geared-motor which is assembly composed of the reduction gear-head 51 and the motor unit 50. The flange face 7b of the bracket 7 and a flange face 3c of the frame 3 are substantially on the same level.
The above-mentioned conventional sealing construction of the geared-motor shown in FIG. 5, however, has a disadvantage that the O-ring 20, which is laid on a corner of the outer face 7d and the flange face 7b of the bracket 7, is liable to be easily displaced upward even by a light touch of a finger before or when the reduction gear-head 51 is coupled to the motor unit 50. This is because a height "B" designated in FIG. 5 of the circular boss 7c is small because of the miniaturization of the geared-motor. And furthermore, the O-ring 20 is easily caught by a finger at the inner edge of the flange face 3c when the reduction gear head 51 is coupled to the motor unit 50. Furthermore, the O-ring 20 can easily slip off from an open end part 7f of the circular boss 7c when the reduction gear head 51 is detached from the motor unit 50.
If the reduction gear head 51 and the motor unit 50 are coupled under a condition where the O-ring 20 is missings or has been slipped off, the sealing of the reduction gear-head 51 and the motor unit 50 is not completed, because either the O-ring 20 is missing or is misaligned, and hence does not serve as a sealing member. As a result, the lubricant grease 15 in the reduction gear head leaks out to the outside of the gear case 2 or to the inside of the motor unit 50.